'-GTIQII   OF  STOCKS    III   CITRUS  F. 

By 

Herbert   JohnlTebber* 
r.    of   Calif.  Agric.   Sept.   Sta.    Bui.    317 


THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

LOS  ANGELES 


OWIVEBSITY  OF    CALIFORNIA   PUBLICATIOH8 


COLLEGE  OF  AGRICULTURE 


AGRICU  TURAL  EXPERIMENT  STATION 


BERKELEY,  CALIFORNIA 


SELECTION  OF  STOCKS  IN 
CITRUS   PROPAGATION 


BY 
HERBERT  JOHN  WEBBER 


ILVIStON  OF  SUBTROPICAL  HORTlCULTUftt 

COLLEGE  OF  AGRICULTURE 

BERKELEVCALIFORNIA 


BULLETIN  No.  317 

JANUARY,  1920 


UNIVERSITY  OF  CALIFORNIA  PRESS 
BERKELEY 

1920 


EXPERIMENT  STATION  STAFF 
HEADS  or  DIVISIONS 

DAVID  P.  BARROWS,  Ph.D.,  LL.D.,  President  of  the  University. 

THOMAS  FORSYTH  HUNT,  Dean. 

EDWARD  J.  WICKSON,  Horticulture  (Emeritus). 

WALTER  MULFORD,  Forestry,  Director  of  Resident  Instruction. 

HERBERT  J.  WEBBER,  Director  Agricultural  Experiment  Station. 

B.  H.  CROCHERON,  Director  of  Agricultural  Extension. 
HUBERT  E.  VAN  NORMAN,  Vice-Director;  Dairy  Management. 

JAMES  T.  BARRETT,  Acting  Director  of  Citrus  Experiment  Station;  Plant  Pathology. 
WILLIAM  A.  SETCHELL,  Botany. 
MYER  E.  JAFTA,  Nutrition. 
CHARLES  W.  WOODWORTH,  Entomology. 
RALPH  E.  SMITH,  Plant  Pathology. 
J.  ELIOT  COIT,  Citriculture. 
JOHN  W.  GILMORE,  Agronomy. 
CHARLES  F.  SHAW,  Soil  Technology. 
JOHN  W.  GREGG,  Landscape  Gardening  and  Floriculture. 
FREDERIC  T.  BIOLETTI,  Viticulture  and  Enology. 
WARREN  T.  CLARKE,  Agricultural  Extension. 
JOHN  S.  BURD,  Agricultural  Chemistry. 
CHARLES  B.  LIPMAN,  Soil  Chemistry  and  Bacteriology 
CLARENCE  M.  HARING,  Veterinary  Science  and  Bacteriology. 
ERNEST  B.  BABCOCK,  Genetics. 
GORDON  H.  TRUE.  Animal  Husbandry. 
FRITZ  W.  WOLL,  Animal  Nutrition. 
W.  P.  KELLEY,  Agricultural  Chemistry. 
H.  J.  QUAYLE,  Entomology. 
ELWOOD  MEAD,  Rural  Institutions 
H.  S.  REED,  Plant  Physiology. 
J.  C.  WHITTEN,  Pomology. 
fFRANK  ADAMS,  Irrigation  Investigations. 

C.  L.  ROADHOUSE,  Dairy  Industry. 
R.  L.  ADAMS,  Farm  Management. 

F.  L.  GRIFFIN,  Agricultural  Education. 
JOHN  E.  DOUGHERTY,  Poultry  Husbandry. 
S.  S.  ROGERS,  Olericulture. 
L.  J.  FLETCHER,  Agricultural  Engineering. 
EDWIN  C.  VOORHIES,  Assistant  to  the  Dean. 


t  In  co-opermtion  with  office  of  Public  Road*  and  Rural  Engineering,  U.  8.  Department  of 
Agriculture. 


SELECTION  OF  STOCKS  IN  CITRUS  PROPAGATION* 

BY  HERBERT  JOHN  WEBBER 


CONTENTS 

PAGE 

Forebrief 269 

Statement   of   problem 270 

Stocks  used  in  citrus  propagation 272 

Growing    nursery    stock 272 

Experiments  with  different-sized  nursery  trees 273 

History  of  trees  used  in  experiment 273 

Comparative  tests  of  large,  intermediate,  and  small  nursery  trees 275 

Discussion  of  results 282 

Variations  in  sweet  and  sour  orange  seedlings 284 

Size  variations  in  budding-stock  seedlings 290 

Examination  of  evidence  and  conclusion 295 

Recommendations   ..  -  300 


FOREBRIEF 

Nursery  trees  even  when  grown  from  selected  buds  taken  from 
selected  trees  differ  greatly  in  size  when  they  reach  transplanting 
age.  Commonly  the  large  trees  are  sold  first  and  the  small  trees  later 
when  they  reach  the  required  size. 

Large,  medium,  and  small  nursery  trees  of  Washington  navel  and 
Valencia  oranges  and  Marsh  grapefruit  grown  in  comparative  tests 
show  that  after  2y2  years  in  the  orchard  the  large  trees  remain  large, 
the  intermediate  remain  intermediate,  and  the  small  remain  small. 
The  evidence  indicates  that  this  condition  is  inherent  in  the  trees  and 
that  in  planting  orchards  only  the  large  nursery  trees  should  be  used. 

An  examination  of  sweet  and  sour  orange  seedling  stock,  such  as 
is  used  for  budding,  showed  the  presence  of  many  widely  different 
types.  Some  of  these  types  were  propagated  and  the  trees  at  the  end 
of  41/2  years  still  show  the  same  marked  difference.  Some  are  fully 
5  times  as  large  as  others.  Yet  all  such  types  are  used  as  stocks. 

Budding  on  seedling  stocks  of  different  types  and  unknown  char- 
acter of  growth  is  believed  to  be  largely  responsible  for  the  different 
sizes  of  budded  trees  developed  in  the  nursery  and  also  for  many  of 
the  irregularities  in  size  and  fruitfulness  of  orchard  trees. 

*  Paper  No.  63,  University  of  California,  Graduate  School  of  Tropical  Agri- 
culture and  Citrus  Experiment  Station,  Riverside,  California. 

DIVISION  OF  SUBTROPICAL  HORTICULTURE 
210379  '      COLLEGE  OF  AGRICULTURE 
BERKELEY,  CAUFORW* 


270  UNIVEBSITY  OP  CALIFORNIA — EXPERIMENT  STATION 

This  discovery  nu-ans  that  nursery  methods  should  be  changed. 

1.  Seeds  for  growing  nursery  stock  must  be  taken  from  carefully 
selected  good  trees  of  the  kind  desired. 

2.  When  transplanting  from  the  seed  bed  to  the  nursery  all  small 
seedlings,  probably  50  per  cent  of  the  total  number,  should  be  dis- 
carded. 

3.  Nurseries  should  be  inspected  before  budding  and  all  small  and 
inferior  plants  cut  out. 

4.  When  budded  trees  reach  the  age  for  transplanting  into  the 
orchard,  only  the  good,  vigorous-growing  ones  should  be  used. 

The  nursery  methods  suggested  will  probably  be  found  to  be 
equally  applicable  and  important  in  the  growing  of  nursery  stock 
of  apples,  peaches  and  other  trees  propagated  by  budding. 

If  these  statements  appeal  to  you  as  being  of  interest,  read  what 
follows. 

STATEMENT   OF    PROBLEM 

Citrus  growers  throughout  the  state  have  observed  great  variation 
in  the  yield  of  different  trees  in  the  same  orchard.  This  variation  is 
known  to  be  universal  even  in  groves  of  the  same  variety  that  have 
been  planted  with  the  best  obtainable  nursery  trees.  Some  groves 
have  been  studied  in  which  all  of  the  trees  were  quite  uniform  and 
fairly  productive,  yet  a  variation  in  yield  uniformly  occurred.  Other 
groves  were  found  to  be  very  irregular,  containing  many  trees  that 
made  a  very  unsatisfactory  and  slow  growth,  and  these  were  mixed 
irregularly  with  others  that  were  somewhat  better  and  still  others  that 
were  good-growing,  vigorous  trees,  that  yielded  well.  Batchelor  and 
Reed  have  shown  that  the  yields  of  trees  in  the  most  uniform  groves 
will  vary  from  30  to  40  per  cent  of  the  mean. 

The  margin  of  profit  is  not  so  great  in  the  citrus  industry  that 
growers  can  afford  to  be  indifferent  to  such  conditions.  It  is  of  the 
highest  importance  that  every  tree  should  be  a  good  producer  and 
pay  its  share  of  profit.  The  very  careful  records  of  individual  tree 
production  that  have  been  made  through  periods  of  several  years  on 
the  same  trees  by  Mr.  A.  D.  Shamel  of  the  U.  S.  Department  of  Agri- 
culture and  his  assistants  have  abundantly  demonstrated  the  very 
real  and  vital  importance  of  this  problem.  Citrus  growers  in  general 
recognize  the  importance  of  the  problem  and  are  keenly  alive  to 
the  necessity  of  remedying  the  conditions  as  far  as  the  knowledge 
available  will  permit. 


BULLETIN  317     SELECTION  OP  STOCKS  IN  CITRUS  PROPAGATION  271 

Mr.  Shamel  has  studied  the  importance  of  taking  buds  from  good 
bearing  trees  known  to  be  productive  and  true  to  type  and  has  advo- 
cated a  method  of  bud  selection  based  on  careful  tree  records.  This 
investigation  was  of  great  importance  to  the  industry  and  the  method 
of  bud  selection  advocated  has  been  generally  adopted. 

There  can  be  no  doubt  that  as  emphasized  by  Shamel  the  use  of 
buds  taken  indiscriminately  without  any  care  except  to  see  that  they 
were  of  a  certain  known  variety  is  responsible  for  much  of  the  varia- 
tion in  production  as  well  as  in  type  that  occurs  in  orchards.  When, 
however,  an  analysis  is  made  of  the  factors  influencing  yield,  it 
seems  probable  that  this  is  only  one  of  several  factors  that  need  to 
be  considered. 

The  variations  in  yield  of  trees  of  the  same  variety  in  the  same 
orchard,  planted  at  the  same  time  and  cultivated  and  treated  as  nearly 
alike  as  possible  are  likely  to  be  due  primarily  to  one  of  the  follow- 
ing factors:  (1)  to  variations  inherent  in  the  buds  due  to  different 
heritage;  (2)  to  different  kinds  and  characters  of  stock  used;  (3)  to 
the  character  of  the  union  obtained  in  the  budding  or  grafting;  (4) 
to  differences  in  the  individual  environment,  especially  as  to  soil, 
under  which  the  trees  are  growing;  and  (5)  to  accidental  and 
unavoidable  differences  in  the  treatment  given  different  trees.  The 
first  of  these  factors  has  been  thoroughly  studied  and  emphasized  by 
Shamel  and  need  be  given  no  further  consideration  here.  The  influence 
of  the  character  of  the  stock  on  this  variation  is  believed  by  the  writer 
to  be  very  important  and  fundamental,  and  the  discussion  of  experi- 
ments and  observations  on  this  factor  form  the  basis  of  this  bulletin. 

The  writer  desires  to  explain  that  this  bulletin  should  be  con- 
sidered largely  as  a  report  of  progress  as  the  experiments  and  studies 
have  not  been  completed  and  will  not  be  for  several  years.  The  results 
already  obtained  have  begun  to  attract  the  attention  of  growers,  how- 
ever, and  the  improved  nursery  methods  suggested  by  the  writer  are 
already  coming  to  be  used.  The  general  adoption  of  these  methods  is 
believed  by  the  writer  to  mean  so  much  to  the  fruit  interests  of  the 
country  that  he  feels  that  he  is  no  longer  justified  in  withholding  the 
results  and  suggestions  from  publication,  even  though  the  evidence  is 
not  yet  entirely  complete. 

It  is  important  to  emphasize  that  while  both  the  nature  of  the  bud 
and  of  the  stock  is  important,  all  of  the  variations  in  yield  found  in 
orchards  certainly  are  not  due  to  these  factors.  The  other  factors 
mentioned  doubtless  also  have  an  important  influence  on  the  yields  of 
different  trees  in  orchards. 


272  UNIVERSITY  OP  CALIFORNIA — EXPERIMENT  STATION 

STOCKS    USED    IN    CITRUS    PROPAGATION 

The  stocks  used  in  citrus  propagation  in  California  are  mainly 
seedlings  of  the  sweet  orange  (Citrus  sinsnsis),  the  sour  orange  (Citrus 
Auranthtm),  the  grape  fruit  or  pomelo  (Citrus  yrandis)  and  the 
Trifoliate  orange  (Ponrirus  trifoliata).  Certain  varieties  of  the  lemon 
(Citrus  Linumia}  such  as  the  Florida  rough  lemon  and  the  Chinese 
lemon  have  been  used  to  some  extent  but  scarcely  more  than  in  an 
experimental  way.  A  discussion  of  the  comparative  merits  of  these 
various  types  of  stocks  will  be  found  in  Bulletin  267  of  this  station, 
prepared  by  Messrs.  Bonus  and  Mertz. 

The  sweet  and  sour  orange  stocks  are  the  types  almost  universally 
used  and  probably  98  per  cent  of  the  groves  of  California  are  budded 
on  either  one  or  the  other  of  these  two  stocks.  Almost  no  attention 
has  been  given  to  the  source  or  kind  of  seed  used  in  growing  the 
stocks.  The  seeds  of  the  sweet  orange  used  for  growing  seedlings  to 
be  budded  have  been  taken  indiscriminately  from  almost  any  sweet 
orange  tree  that  produced  seedy  fruit.  The  sour  orange  seed  used 
has  been  obtained  mainly  from  Florida,  where  it  is  gathered  from 
numerous  seedling  trees  of  the  sour  oranges  that  are  grown  here  and 
there  over  the  state,  one  or  two  occurring  in  almost  every  yard.  This 
orange  is  used  commonly  in  Florida  as  a  home  fruit  in  making  orange- 
ade and  marmalade. 

GROWING  NURSERY  STOCK 

In  growing  nursery  stock  the  seed  is  usually  grown  in  a  well 
prepared  seed  bed  that  is  protected  from  full  exposure  to  the  sun  by 
a  slat  shed  or  by  a  burlap  or  cloth  shade.  The  seed  is  drilled  about 
1  inch  apart  in  rows  about  12  inches  apart,  and  grown  in  this  way 
for  about  one  year,  when  they  are  transplanted  into  the  nursery.  At 
the  time  of  transplanting,  the  seedlings  usually  vary  greatly  in  size, 
ranging  from  a  few  inches  to  a  foot  or  even  18  inches  or  more  in 
height,  depending  on  the  soil  in  which  they  are  grown  and  other 
conditions.  This  variation  in  height,  however,  invariably  occurs. 
In  ordinary  practice  all  of  the  seedlings  are  transplanted  or  at  most 
only  a  few  of  the  smaller  ones  are  discarded. 

In  the  nursery  the  seedlings  are  planted  about  1  foot  apart  in  rows 
from  3  to  4  feet  apart,  and  must  grow  a  year  or  more  before  they  reach 
sufficient  size  for  budding.  They  are  usually  planted  into  the  nursery 
in  the  spring  and  budded  the  following  spring  a  year  later.  When 
the  budding  begins  there  is  usually  considerable  variation  in  the 


BULLETIN  317     SELECTION  OP  STOCKS  IN  CITRUS  PROPAGATION  273 

size  of  the  seedlings  and  frequently  the  largest  ones  that  have  reached 
sufficient  size  are  budded  and  those  that  are  too  small  are  allowed 
to  grow  for  several  months  longer,  and  are  budded  when  they  have 
reached  the  desired  size. 

After  budding  the  young  trees  are  preferably  allowed  to  grow  in 
the  nursery  until  they  are  2  years  old  from  the  time  of  inserting  the 
buds,  when  they  are  expected  to  be  ready  to  set  in  the  grove.  At  this 
time,  even  though  they  were  all  budded  at  the  same  time  and  on 
seedlings  of  the  same  age,  they  commonly  vary  greatly  in  size.  Citrus 
trees  are  commonly  sold  according  to  the  diameter  of  trunk  an'd  it 
is  not  an  uncommon  practice  to  go  through  the  nursery  and  first  dig 
and  sell  the  largest  trees,  the  remaining  trees  being  dug  and  sold 
when  they  reach  the  required  size.  If  time  enough  is  given,  the 
smallest  trees  from  the  smallest  stocks  will  finally  reach  sufficient  size 
and  ultimately  all  find  their  way  into  some  orchard  of  the  state. 

Is  the  small  tree  that  requires  a  much  longer  time  to  reach  the 
required  size  for  transplanting  as  likely  to  produce  a  good  productive 
orchard  tree  as  the  vigorous-growing  one  that  first  reached  the  required 
size?  Some  growers  assert  that  the  small  buds  make  just  as  good 
trees  as  the  large  buds.  Apparently,  however,  this  assertion  is  not 
based  on  definite  knowledge,  and  it  would  seem  to  be  contrary  to  our 
general  understanding  of  nature.  It  is  certainly  an  important  ques- 
tion to  determine  as  the  value  of  a  grove  depends  upon  the  character 
of  the  trees  in  it.  So  far  as  the  writer  can  learn,  no  definite  study 
of  this  question  has  been  made  with  any  orchard  fruit  and  almost 
no  evidence  is  evailable  to  assist  in  reaching  a  decision. 

EXPERIMENTS    WITH    DIFFERENT-SIZED    NURSERY    TREES 

History  of  Trees  Used  in  Experiments. — The  plans  for  the  investi- 
gational  work  at  the  Citrus  Experiment  Station  included  the  installa- 
tion of  a  long-time  fertilizer  experiment  which  should  be  very  carefully 
planned  to  avoid  all  mistakes  so  far  as  possible.  It  was  recognized 
that  one  of  the  necessities  of  the  experiment  was  to  secure  uniform 
nursery  trees  in  order  to  render  the  trees'  in  all  plots  as  nearly  equal 
in  their  yielding  capacity  as  possible  and  thus  reduce  to  a  minimum 
the  differences  in  yield  of  the  plots  due  to  individual  tree  variations. 
The  station  thus  decided  to  grow  its  own  nursery  trees  for  the  experi- 
ment in  order  to  be  certain  of  the  history  and  treatment  of  the  trees. 
It  was  decided  to  use  sweet  orange  stock  for  all  of  the  orange  and  grape- 
fruit trees  in  the  experiment  and  sour  orange  stocks  for  the  lemons. 
In  order  to  save  time  seed-bed  stock  of  sweet  and  of  sour  orange 


274  UNIVERSITY   OF   CALItX>RNIA — EXPERIMENT   STATION 

ready  to  set  in  the  nursery  was  purchased  and  planted  in  a  nursery 
in  the  spring  of  1914. 

Attention  not  having  been  directed  at  this  time  to  the  possible 
importance  of  the  source  of  the  seed,  no  special  inquiry  was  made  as 
to  where  the  seed  used  in  growing  the  stock  was  obtained,  special  care 
only  being  taken  to  see  that  the  stock  in  each  case  was  not  mixed 
and  was  of  good  grade.  The  sweet  orange  seed  used  was  probably 
from  sweet  seedlings,  many  of  which  are  still  grown  in  the  vicinity 
of  Riverside,  where  the  nursery  bed  stock  was  grown.  The  seed  for 
the  sour  stock  came  from  Florida  but  nothing  further  was  definitely 
ascertained.  In  each  case  the  seed-bed  stock  purchased  was  in  good 
condition  and  was  in  no  way  different  so  far  as  could  be  determined 
from  the  ordinary  stock  of  these  kinds  usually  used  in  the  state  for 
propagation. 

This  stock  whe  i  dug  from  the  seed  bed  was  sorted  and  all  of  the 
small  seedlings  discarded.  In  this  process  about  15  per  cent  of  the 
sweet  stocks  were  discarded  and  about  25  per  cent  of  the  sour  stocks. 
The  sour  stocks  were  thicker  in  the  seed  bed  than  were  the  sweet  stocks 
and  the  larger  percentage  discarded  as  below  size  was  probably  due 
to  this  cause.  The  seedlings  were  planted  in  rows  in  the  nursery  in  the 
ordinary  form,  the  plants  being  about  12  inches  apart  in  the  rows. 
The  nursery  throughout  was  treated  as  uniformly  as  possible  and  made 
a  good  growth. 

The  trees  were  budded  in  the  spring  of  1915,  about  4000  buds  each 
of  Washington  navel  and  Valencia  oranges  and  Marsh  grapefruit 
being  inserted  on  sweet  stocks  and  4000  Eureka  lemons  on  sour  stock. 
During  the  process  of  budding  again  some  of  the  small  weak  stocks 
that  had  not  made  a  good  growth  were  discarded. 

It  was  of  primary  importance  in  the  experiments  to  secure  buds 
that  could  be  expected  to  give  good  and  uniform  results,  and  through 
the  kindness  of  Mr.  A.  D.  Sharnel  and  the  growers  cooperating  with 
him  in  his  bud  selection  experiments,  the  buds  of  all  the  varieties 
used  were  cut  from  bearing  trees  on  which  records  of  yield  and  type 
of  fruits  produced  had  be.en  kept  through  a  period  of  5  years  and 
which  were  known  in  every  case  to  be  high  yielders  and  of  the  standard 
type  of  each  variety.  The  buds  which  were  all  cut  by  Mr.  Shamcl 
and  Mr.  W.  M.  Mertz,  then  Superintendent  of  Cultivations  in  the 
Citrus  Experiment  Station,  were  in  the  case  of  the  Washington  navel 
and  Eureka  lemon  taken  from  trees  in  groves  belonging  to  the  National 
Orange  Company  at  Riverside.  The  Valencia  buds  were  taken  from 
selected  trees  on  the  Slosson  grove  at  Azusa  and  those  of  the  Marsh 
grapefruit  from  the  grove  of  L.  V.  W.  Brown  of  Riverside.  The 


BULLETIN  317    SELECTION  OF  STOCKS  IN  CITRUS  PROPAGATION  275 

station  is  under  great  obligation  to  all  of  these  gentlemen  for  their 
kind  and  liberal  cooperation. 

The  budding  was  all  done  during  May  and  occupied  a  period  of 
about  2  weeks.  An  excellent  stand  was  obtained  and  the  buds  started 
vigorously  and  as  uniformly  as  could  be  expected.  There  was  con- 
siderable variation  in  the  size  of  the  buds  at  first  due  to  slight  differ- 
ences in  the  promptness  of  different  buds  in  starting  growth,  but  the 
difference  gradually  became  less  marked.  Throughout  the  growth 
of  the  nursery  it  was  recognized  by  all  who  examined  it  critically  as 
an  exceptionally  good  and  uniform  nursery. 

Comparative  Tests  with  Large,  Intermediate,  and  Small  Nursery 
Trees. — In  June  of  1917  when  the  buds  were  two  years  old  they  were 
used  in  planting  the  experimental  grove  on  the  Experiment  Station 
Farm.  A  larger  number  of  trees  were  grown  than  was  needed  for  the 
planting  and  in  digging  and  balling,  those  buds  that  were  under 
average  size  were  discarded.  About  15  per  cent  of  the  trees,  it  is 
estimated,  were  discarded  at  this  time  as  being  undersized. 

The  important  fact  that  the  writer  desires  to  emphasize  in  con- 
nection with  the  growing  of  this  lot  of  nursery  trees  is  that  although 
much  more  than  ordinary  care  was  taken  at  every  step  to  reduce 
the  amount  of  variation  through  using  selected  good-sized  stocks  and 
buds  from  highly  selected  trees,  that,  nevertheless,  when  the  buds 
were  2  years  old  and  ready  to  transplant  into  the  grove,  they  showed 
considerable  variation  in  size.  In  examining  the  nursery  at  this  time 
with  reference  to  what  trees  to  use  in  the  experimental  orchard,  the 
writer  was  impressed  by  the  extent  of  the  variation  in  size  and  con- 
ceived the  idea  of  testing  comparatively  the  different-sized  trees  to  see 
whether  the  size  in  the  nursery  could  be  taken  as  an  indication  of 
what  the  trees  would  later  do  in  the  permanent  orchard. 

In  carrying  out  this  experiment,  18  small,  18  medium,  and  18  large 
trees  were  chosen  by  the  writer  with  the  assistance  of  Mr.  Mertz  from 
each  of  the  varieties  in  the  nursery — Washington  navel  orange, 
Valencia  orange,  Marsh  grapefruit,  and  Eureka  lemon.  In  making 
these  selections  of  large,  medium  and  small  buds  it  was  observed  that 
the  greatest  range  of  variation  apparently  existed  among  the  Wash- 
ington navel  buds  and  the  least  among  the  Valencia  buds.  While  no 
exact  statistical  data  were  obtained  from  which  to  derive  definite 
conclusions,  the  rank  of  extent  of  variation  among  the  buds  of  the 
4  varieties  appeared  to  be  as  follows:  (1)  Washington  navel,  (2) 


276  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION 

Marsh  pomelo,  (3)  Eureka  lemon,  (4)  Valencia.     What  this  means, 
if  it  means  anything,  cannot  now  be  explained. 

In  order  to  determine  whether  the  size  of  the  bud  growth  in  any  of 
the  chosen  plants  might  be  due  to  accidents  to  the  roots,  such  as  injury 
by  gophers,  disease  of  any  kind,  or  to  the  so-called  "bench  root,"  the 
trees  were  dug  and  transplanted  with  bare  roots  (not  balled)  and 
the  roots  of  every  tree  were  examined  carefully  and  notes  made 
regarding  the  growth.  None  of  the  trees  dug  and  so  examined  showed 
any  indication  of  injury  or  disease  that  might  be  considered  as 
having  influenced  the  growth.  In  all  cases  the  roots  appeared  to  be 
thoroughly  vigorous  and  healthy. 

The  trees  were  planted  in  soil  that  had  never  grown  a  tree  crop 
and  which  was  considered  fairly  uniform  and  suitable  for  the  experi- 
ment. They  were  set  in  rows  24  feet  apart  and  the  trees  10  feet  apart 
in  the  rows.  The  Washington  navels,  Valencias,  and  Marsh  grape- 
fruits were  so  arranged  that  in  the  first  row  came  the  18  large 
trees,  in  the  second  row  the  18  small  trees,  and  in  the  third  row  the 
18  intermediate-sized  trees. 

Shortly  after  the  trees  were  set  in  the  permanent  orchard  caliper 
measurements  of  the  diameter  of  the  trunk  of  each  tree  were  made 
at  a  point  about  6  inches  above  the  point  of  union  of  bud  and  stock, 
the  point  where  the  measurements  were  taken  being  marked  by  a 
band  about  y2  inch  wide  painted  on  the  trunk.  The  average  of  these 
measurements  for  each  different  group  is  given  in  table  1,  which 
will  be  discussed  later. 

The  .Eureka  lemon  trees  for  some  reason  did  not  stand  the  trans- 
planting very  well  and  so  many  of  them  died  or  were  injured  that 
the  entire  lot  was  later  discarded  and  taken  out. 

The  orchard  containing  these  trees  has  been  given  as  nearly 
uniform  treatment  as  possible  in  order  that  any  variation  occurring 
in  the  growth  of  the  different  trees  might  be  considered  as  primarily 
dufi  to  inherent  differences  in  the  trees  themselves. 

"  The  trees  have  now  been  growing  in  the  orchard  slightly  over  2 
years  and  have  made  excellent  progress.  The  large  trees  in  every 
case  would  now  be  considered  to  be  rather  larger  than  usual  for  2-year- 
old  trees  and  the  intermediate  and  small  trees  have  in  general  grown 
in  about  the  same  ratio  proportionately  to  their  size.  The  differences 
in  size  that  were  exhibited  in  the  trees  when  they  were  planted  are 
today  just  as  marked  as  they  were  in  the  beginning. 

The  Washington  navels  all  budded  on  sweet  stocks  show  as  in  the 
nursery  rather  the  most  striking  difference.  All  of  the  18  large  trees 


BULLETIN  317     SELECTION  OF  STOCKS  IN  CITRUS  PROPAGATION 


277 


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UNIVERSITY   OP   CALIFORNIA — EXPERIMENT   STATION 

continue  to  be  large  and  this  spring  (the  second  spring)  bloomed 
heavily  and  set  some  fruit.  The  intermediate-sized  trees  still  retain 
their  same  comparative  size  and  while  they  produced  some  flowers  have 
set  fruit  on  only  one  tree.  The  small  trees,  while  they  look  healthy 
and  have  grown  in  about  the  same  proportion  as  the  large  trees,  are 
all  of  them  still  small.  They  produced  little  bloom  and  no  fruit.  The 
proportionate  size  of  these  trees  can  be  observed  clearly  by  an  exam- 
ination of  Fig.  1. 

In  order  to  illustrate  more  clearly  the  comparative  sizes  of  these 
three  groups  of  trees,  photographs  were  taken  of  an  individual  tree 
in  each  group:  (large,  small,  and  intermediate)  which  was  judged  to 
represent  about  the  average  size  of  the  group.  These  photographs 
are  reproduced  in  Fig.  2. 

The  Valencias  all  budded  on  sweet  stocks  show  less  marked  differ- 
ences in  size  between  the  large,  intermediate,  and  small  trees  than 
the  navels,  but  the  differences  are  great  enough  to  show  clearly,  as 
will  be  seen  by  an  examination  of  Fig.  3.  The  Valencias  have  in 
general  grown  well  and  within  each  group  of  large,  small,  and  inter- 
mediate trees  there  is  not  very  wide  variation.  The  comparative  size 
of  average  trees  from  each  group  is  illustrated  in  Fig.  5.  The  trees 
in  the  group  of  large  Valencias  developed  some  bloom  last  spring 
(the  second  spring)  but  did  not  set  fruit.  Some  little  bloom  was 
developed  on  trees  in  the  other  two  groups,  but  in  neither  case  was 
it  anywhere  near  so  abundant  as  in  the  group  of  large  trees,  and 
no  fruit  set. 

The  Marsh  seedless  grapefruit  trees  budded  on  sweet  stocks  as  in 
the  case  of  the  navels  and  Valencias  continue  to  show  differences  in 
size  between  the  three  groups,  large,  small,  and  intermediate,  but  the 
difference  is  not  so  great  as  in  the  case  of  the  navels  and  Valencias. 
As  a  whole,  the  grapefruit  trees  have  not  made  as  good  a  growth  as  the 
orange,  and  several  trees  died  as  a  result  of  the  shock  of  transplanting 
with  "bare  root"  in  July.  The  fact  remains,  however,  that  after  2 
years'  growth  in  the  orchard,  all  of  the  trees  continue  to  retain  their 
same  relative  size.  (Compare  Fig.  4.)  The  comparative  size  of 
average  trees  from  each  group  is  shown  in  Fig.  6.  Only  a  few  flowers 
developed  on  these  grapefruits  last  spring  and  but  very  few  fruits  set. 

One  of  the  most  reliable  indications  of  comparative  growth  and 
size  is  the  change  in  size  of  trunk  as  indicated  by  the  diameter  or 
circumference  at  a  certain  definite  point,  and  in  Table  1  is  given  the 
average  caliper  measurements  of  the  diameter  of  the  trees  of  each 
group  of  each  variety  taken  July,  1917,  a  few  days  after  the  trees 


BULLETIN  317     SELECTION  OF  STOCKS  IN  CITRUS  PROPAGATION 


279 


IfNIVERSITY   OP   CAUFORNI.V — EXPERIMENT   STATION 

were  planted,  in  comparison  with  similar  average  measurements  of 
diameter  taken  April,  1919,  at  the  same  points  on  each  tree  trunk, 
the  measurements  being  in  centimeters. 

TABLE  1 

AVERAGE  DIAMETER  OK  TRUNKS  (IN  CENTIMETERS)  OF  LARGE,  INTERMEDIATE,  AND 

SMALL  TREES 

Navels 
Large  Intermediate  Small 

July,  1917  „ 2.53  1.69  1.29 

April,  1919  3.79  2.60  2.16 

Percent  of  increase 49.8  53.8  67.4 

Valencia* 

July,  1917  2.58  l.(51  1.16 

April,  1919  3.30  2.52  2.15 

Percent  of  increase 27.9  56.5  85.3 

Grapefruit 

July,  1917  3.11  1.87  1.05 

April,  1919  3.29  2.48  1.84 

Percent  of  increase 5.8  32.6  75.2 

It  will  be  seen  from  an  examination  of  the  above  table  that  in  each 
group  the  difference  in  sizes  still  remains  very  marked.  The  inter- 
mediate and  small  groups  have  made  a  larger  percentage  of  increase 
in  size  as  indicated  by  diameter  than  have  the  large  trees,  but  in 
judging  the  meaning  of  these  figures  it  should  be  remembered  that 
the  rate  of  growth  as  measured  by  diameter  of  trunk  and  estimated 
in  this  way  does  not  show  the  relative  differences  very  clearly,  as  much 
more  growth  is  necessary  to  cover  a  large  trunk  a  certain  thickness 
than  is  required  to  cover  a  small  trunk  the  same  thickness. 

In  general,  it  may  be  said  that  each  group  is  in  size  about  2  years 
behind  the  next.  It  will  be  noted  that  the  intermediate  trees  in  1919 
are  in  each  variety  about  the  same  size  as  the  large  trees  were  in 
1917  and  the  small  trees  in  1919  are  about  the  same  size  that  the 
intermediate  were  in  1917. 

If  it  were  possible  to  get  the  volume  occupied  by  each  tree  this 
would  be  a  better  indication  of  the  comparative  size,  but  no  accurate 
measure  of  this  kind  can  be  obtained.  To  get  as  nearly  as  possible 
a  comparison  of  this  kind,  in  April,  1919,  the  top  of  each  tree  was 
measured  in  three  directions,  getting  the  diameter  of  spread  through 
the  top  east  and  west,  north  and  south,  and  from  the  first  branch  up 


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UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION 

through  the  top.  These  figures  multiplied  together  give  an  arbitrary 
figure  that  represents  fairly  accurately  the,  comparative  volume  of 
the  top.  As  a  check  on  the  accuracy  of  such  figures  a  number  of 
trees  were  examined  and  graded  in  rank  of  size  as  accurately  as  could 
be  done  by  the  eye,  using  the  greatest  caution.  These  judgments 
corresponded  very  accurately  with  the  figures  obtained  by  the  meas- 
urements. While  admittedly  such  figures  are  not  accurate  measures, 
they  are  believed  to  represent  the  comparative  size  of  the  trees  fairly 
closely.  The  averages  obtained  for  each  group  of  trees  are  given 
in  Table  2. 

TABLE  2 

AVERAGE  COMPARATIVE  SIZE  (IN  CUBIC  INCHES)  or  TREE  TOPS  AS  INDICATED  BY 

PRODUCT  or  EAST  AND  WEST  DIAMETER  X  NORTH  AND  SOUTH  DIAMETER 

X  HEIGHT  FROM  FIRST  BRANCH  TO  TOP 


Navels    

Valencias  . 
Grapefruit 


Large 

Intermediate 

Small 

54,174 

20,185 

12,541 

29,003 

15,606 

12,953 

26,343 

15,827 

10,642 

Discussion  of  Results. — The  illustrations  and  data  given  clearly 
show  that  after  2  years'  growth  in  the  orchard,  the  large,  intermediate 
and  small  trees  retain  the  same  relative  size  that  they  had  when  dug 
from  the  nursery.  An  examination  made  very  recently  (November  1, 
1919),  6  months  after  the  data  given  were  taken,  shows  clearly  that 
the  same  conditions  still  exist.  It  is  possible  that  in  several  years  some 
of  the  intermediate  and  small  trees  will  make  good  growth  and  nearly 
or  quite  overtake  the  large  trees  in  size.  However,  it  seems  highly 
improbable,  judging  from  present  indications,  that  very  many  of  them 
will  do  this.  The  slower  growth  of  the  majority  would  seem  to  be  due 
to  some  inherent  cause  that  is  not  likely  to  change  or  to  be  outgrown. 
Which  ones  of  the  possible  factors  influencing  the  size  of  budded  trees 
is  most  likely  to  be  responsible  for  this  different  growth  ?  It  would  not 
seem  to  be  due  in  very  large  degree  to  differences  in  treatment  or  local 
environment,  as  all  trees  in  the  large,  intermediate,  and  small  test  rows 
retain  their  relative  size  relationship  and  this  would  not  be  the  case  had 
any  been  greatly  injured  or  retarded  by  accidental  variations  in  treat- 
ment or  local  soil  irregularities.  Again,  they  exhibited  the  same  varia- 
tion when  in  the  nursery  in  an  entirely  different  soil.  Had  any  local 
soil  condition  in  the  nursery  been  the  cause  of  the  different  growth  rate, 


BULLETIN  317     SELECTION  OF  STOCKS  IN  CITRUS  PROPAGATION 


283 


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284  UNIVERSITY   OP   CALIFORNIA — EXPERIMENT   STATION 

the  trees  would  probably  have  changed  in  their  relation  when  trans- 
planted to  new  soil.  It  is  not  improbable,  however,  that  some  of  the 
variation  may  be  due  to  environment  and  this  possibility  will  be  dis- 
cussed  more  fully  under  another  heading. 

Are  the  variations  due  to  the  character  of  the  union  obtained  in 
budding?  The  evidence  at  hand  is  not  entirely  sufficient  to  enable 
us  to  exclude  this  factor  as  a  possible  cause.  The  bud  unions,  however, 
appear  equally  well  formed  on  all  the  trees  and  this  would  not  seem 
to  be  the  main  cause  of  the  difference  in  growth. 

Can  it  be  that  the  differences  observed  are  due  to  inherent  differ- 
ences of  character  in  the  buds?  This  would  not  seem  to  be  the  case 
in  view  of  the  fact  that  all  buds  used  were  chosen  with  great  care  from 
trees  known  to  be  standard  in  character  and  on  which  production 
records  had  been  taken  through  a  5-year  period.  The  only  other 
factor  to  which  the  variation  might  be  ascribed  is  to  inherent  con- 
stitutional differences  in  the  root-stocks  on  which  the  trees  are  budded. 
This  immediately  leads  to  the  inquiry  as  to  whether  the  stocks  used 
for  propagation  are  ordinarily  sufficiently  variable  in  growth  so  that 
such  differences  might  be  ascribed  to  this  cause. 

VARIATIONS    IN    SWEET   AND    SOUR    ORANGE    SEEDLINGS 

As  explained  in  the  early  part  of  this  paper,  the  only  distinction 
ordinarily  made  in  root-stocks  is  that  one  chooses  either  sweet  or 
sour  orange,  grapefruit,  lemon  or  possibly  trifoliate  orange.  Up 
to  the  present  time  no  other  choice  in  general  has  been  exercised.  It 
is  well  known  that  there  are  hundreds  of  different  variations,  types 
or  varieties  within  eaeh  of  these  species  or  large  groups.  The  great 
majority  of  the  numerous  named  varieties  of  the  sweet  orange  are 
merely  seedling  variations  that  have  been  propagated  by  budding. 
While  there  are  not  so  many  named  varieties  of  the  sour  orange  this 
is  doubtless  due  to  the  fact  that  it  is  not  cultivated  extensively  as  the 
fruit  is  not  in  demand. 

Fortunately,  we  have  obtained  some  evidence  on  this  matter 
through  a  direct  examination  of  seedlings  propagated  for  nursery 
purposes.  In  October,  1914,  the  writer  in  company  with  Messrs. 
W.  M.  Mertz  and  E.  E.  Thomas,  both  then  of  the  Citrus  Experiment 
Station,  were  going  through  a  nursery  of  seedling  sour  and  sweet 
oranges  of  budding  size,  when  our  attention  was  drawn  to  a  type 
markedly  different  from  the  ordinary.  This  was  among  the  sour 
orange  seedlings.  As  a  collection  of  varieties  was  being  made  at  the 
station,  we  conceived  the  idea  of  selecting  the  distinct  types  that  we 


BULLETIN  317     SELECTION  OF  STOCKS  IN  CITRUS  PROPAGATION 


285 


Fig.  5. — Valencia  orange:  average-sized  trees  chosen  from  test  rows  of  large, 
medium,  and  small  nursery  trees:  large,  on  left;  medium,  in  center;  small,  on 
right.  Planted  in  orchard  June,  1917,  and  photographed  May,  1919. 


Fig.  6. — Marsh  seedless  grapefruit:  average-sized  trees  chosen  from  test  rows 
of  large,  medium,  and  small  nursery  trees :  large,  on  left ;  medium,  in  center ; 
small,  on  right.  Planted  in  orchard  June,  1917,  and  photographed  May,  1919. 

could  recognize  clearly  and  of  testing  them  to  see  how  great  differences 
existed.  Sixteen  different  types  of  the  sour  orange  were  chosen  and 
4  different  types  of  the  sweet  orange.  Many  more  distinct  types  could 
doubtless  have  been  selected  but  it  was  not  recognized  at  the  time  that 
the  selection  of  these  types  had  any  more  important  bearing  than 
merely  securing  for  the  variety  orchard  a  few  more  different  forms, 
all  probably  worthless.  Bud  sticks  of  these  16  sour  orange  and  4  sweet 


286 


UNIVERSITY   OP    CALIFORNIA — EXPERIMENT   STATION 


orange  seedlings  were  cut  and  two  trees  budded  of  each  for  trial  in 
the  variety  orchard.  These  trees  budded  on  sour  orange  stock  are 
now  4Vfe  years  old  from  the  bud  and  have  been  2y2  years  planted  in 
the  variety  orchard,  thus  being  the  same  age  as  the  trees  in  the 
experiment  described  above. 


Fig.  7. — Sour  orange  (C.  E.  8.  No.  628).  A  good,  typical  type  with  vigorous 
growth  and  excellent  foliage  and  branching  characters.  Selected  as  a  good 
stock  type.  Compare  size,  branching  and  foliage  with  types  illustrated  in  Figs.  8, 
9,  10,  11,  and  12. 

An  examination  of  these  different  types  now  shows  them  all  to  be 
remarkably  distinct  from  each  other  in  character  and  size  of  growth, 
branching,  foliage  and  other  important  characters.  A  series  of  photo- 
graphs of  6  of  these  different  types  of  sour  orange  is  reproduced  here 
to  illustrate  the  great  difference  in  size  and  character  of  growth. 
Compare  with  each  other  Figs.  7,  8,  9,  10,  11,  and  12.  All  of  the 


BULLETIN  317     SELECTION  OP  STOCKS  IN  CITRUS  PROPAGATION 


287 


trees  shown  in  these  illustrations  were  reduced  the  same  in  photo- 
graphing as  shown  by  the  yard  stick  standing  beside  each  tree.  The 
tree  illustrated  in  Pig.  7  was  selected  as  a  good  typical  type  with 
vigorous  growth  and  good  branching  and  foliage  characters.  This 
is  probably  the  only  one  of  the  series  illustrated  that  would  make  a 
good  stock  to  bud  for  orchard  planting.  No  grower  would  assume- that 
the  trees  illustrated  in  Figs.  8,  10,  11,  and  12  would  give  satisfactory 
results  and  he  would  scarcely  elect  to  bud  the  tree  shown  in  Fig.  9 
because  it  has  variegated  foliage.  The  tree  in  Fig.  8  is  a  small  dwarf 


Fig.  8. — Sour  orange  (C.  E.  S.  No.  619).*  A  slow-growing  dwarf  type.     Com- 
pare size,  branching  and  foliage  with  types  illustrated  in  Figs.  7,  9,  10,  11,  and  12. 

type  with  spreading  habit  and  small  leaves.  In  volume,  this  tree  is 
not  over  one-fifth  of  that  shown  in  Fig.  7.  The  tree  in  Fig.  10  rep- 
resents a  fine  healthy  tree  but  a  dwarfish,  slow  grower  with  small 
leaves  making  a  dense  foliage.  Fig.  12  is  similar  to  Figs.  8  and  10 
in  its  slow  growth  only.  Both  of  the  trees  grown  of  this  type  show 
a  good  many  bare  limbs  as  if  not  thoroughly  strong  and  healthy.  It 
seems  to  have  a  weak  constitution  and  to  easily  shed  its  leaves,  which 
are  characteristically  different  from  those  of  the  other  types.  The 
tree  shown  in  Fig.  11  is  one  of  the  types  having  growth  of  about  an 
intermediate  degree  of  vigor  and  when  seen  in  comparison  with  other 
types  of  the  same  age  can  be  recognized  easily  as  of  an  intermediate 
grade.  If,  however,  such  types  were  compared  only  with  their  own 

DIVISION  OF  SUBTROPICAL  HORTICULTURE 

COLLEGE  OF  AGRICULTURE 

BERKELEY,  CALIFORNIA 


L>ss 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION 


kind,  they  could  not  be  recognized  as  being  of  any  slower  growth 
than  ordinary.  In  some  cases  the  slow  dwarfish  character  of  the  plant 
can  apparently  be  recognized  by  the  smaller  leaves,  shorter  internodes 
and  general  characters  that  indicate  slow  growth,  but  in  very  many 
seedlings  of  intermediate  growth  the  true  character  evidently  cannot 
be  determined  except  by  a  comparison  with  the  growth  of  other 
seedlings  of  the  same  age  grown  on  the  same  soil. 


Fig.  9. — Sour  orange  (C.  E.  3.  No.  618).  A  vigorous-growing  large  type,  but 
differing  from  tree  shown  in  Fig.  7  in  habit  of  growth  and  foliage  characters. 
The  leaves  are  variegated. 

All  of  the  types  illustrated  and  many  more  can  doubtless  be  found 
in  any  ordinary  sour  orange  nursery  and  are  probably  regularly 
budded,  the  trees  sold  and  planted  in  permanent  orchards. 

The  4  variations  or  different  types  of  sweet  seedlings  selected  from 
the  nursery  at  the  same  time  the  sour  orange  types  described  above 


BULLETIN  317     SELECTION  OP  STOCKS  IN  CITRUS  PROPAGATION 


289 


were  selected,  were  also  propagated  and  are  now  4^-year-old  buds. 
They  have  proven  to  be  very  distinct  in  character  of  foliage  and  rate 
of  growth.  All  4  were  comparatively  slow-growing  types  as  shown 
by  their  size  now  in  comparison  with  buds  of  other  sweet  oranges 
budded  at  the  same  time.  Of  these  types  0.  E.  S.  No.  604  had  small, 
short,  oblong  or  eliptical  leaves  with  rounded  apex  and  short  petioles. 
C.  E.  S.  No.  605  had  similarly  shaped  leaves  to  C.  E.  S.  No.  604,  but 
they  were  larger  and  the  internodes  of  the  stem  were  short.  C.  E.  S. 
No.  606  had  long,  nearly  lanceolate  leaves  with  broadly  winger  petioles, 


Fig.  10. — Sour  orange  (C.  E.  S.  No.  627).     A  slow-growing  dwarf  tree. 

while  C.  E.  S.  No.  607  had  long  lanceolate  leaves  with  narrowly  winged 
petioles.  These  characters  have  continued  to  show  in  the  trees  and  are 
characteristic  differences  of  the  four  types.  Typical  leaves  of  each 
of  these  types  are  illustrated  in  Fig.  13  under  the  numbers  indicated 
above,  which  are  the  permanent  numbers  in  the  Citrus  Experiment 
Station  Collection  (C.  E.  S.  numbers). 

It  must  be  thoroughly  understood  that  the  4  types  discussed  are 
given  merely  as  illustrations.  A  very  large  number  of  variations  are 
present  in  every  bunch  of  sweet  orange  seedlings  and  could  easily  be 
distinguished  and  propagated  if  desired.  There  is  no  evidence  avail- 
able that  indicates  the  sour  orange  to  be  any  more  variable  than  the 
sweet  orange.  Lemon  seedlings,  grapefruit  seedlings,  indeed  seedlings 
of  any  citrus  species  would  doubtless  show  variability  in  about  equal 


290 


UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION 


proportion.  It  is,  however,  fortunately  true  that  seedlings  from  cer- 
tain trees  are  more  variable  than  seedlings  from  certain  other  trees, 
and  that  we  have  in  this  well  known  condition  of  nature  a  reasonable 
hope  that  good  stock  types  may  ultimately  be  found  that  will  give 
progeny  grown  from  seed  that  will  be  comparatively  uniform  through- 
out and  possibly  not  require  the  discarding  of  very  large  numbers 
such  as  suggested  in  the  following  section. 


Fig.  11. — Sour  orange  (C.  E.  S.  No.  625).  A.  type  of  medium  size  and  rapidity 
of  growth,  also  differing  from  others  in  foliage  and  branching  characters. 

SIZE   VARIATIONS    IN    BUDDING    STOCK    SEEDLINGS 

In  a  nursery  at  the  Citrus  Experiment  Station  grown  from  sour 
orange  seeds  obtained  from  several  California  trees,  an  examination 
made  this  last  spring  (April,  1919)  showed  many  variations  similar 
to  those  illustrated  above.  An  idea  of  this  range  of  variation  may  be 
gained  from  an  examination  of  Fig.  14  showing  7  contiguous  seedlings, 
each  one  of  which  shows  different  characters  even  in  this  young  stage. 
At  this  time  the  large  individuals  in  this  nursery  could  have  been 
budded  but  only  about  one-fourth  of  the  entire  number  would  have 
been  sufficiently  large. 


BULLETIN  317     SELECTION  OF  STOCKS  IN  CITRUS  PROPAGATION 


291 


When  the  seedlings  in  this  nursery  were  being  transplanted  from 
the  seed  bed  in  June,  1918,  the  smallest  were  discarded  and  the 
remainder  were  separated  in  two  groups,  one  of  large  and  the  other 
of  small  plants,  which  were  planted  separately.  The  group  of  small 
plants  contained  only  about  one-third  of  the  total  number  grown.1 
The  separation  was  made  entirely  from  the  practical  standpoint  of 
getting  the  large  stocks  together  and  may  not  have  been  altogether 
consistent  or  accurate ;  nevertheless,  an  examination  made  the  next 


Fig.  12. — Sour  orange  (C.  E.  S.  No.  615).  A  slow-growing  dwarf  type  of  weak 
constitution. 

spring  (April,  1919)  showed  the  plantings  of  large  and  small  seedlings 
to  be  still  markedly  different  in  size. 

Three  hundred  and  one  of  the  large  group  were  measured  and  gave 
an  average  height  of  18.19  inches.  They  were  found  to  range  in  height 
from  5  to  30  inches.  It  is  of  interest  to  know  what  proportion  of  these 
were  of  various  sizes  and  thus  the  measurements  of  the  plants  are 
given  below  (Table  3)  grouped  in  classes  differing  by  2  inches  in 
height.  The  measurements  were  made  in  inches  and  half  inches. 
Each  class  is  inclusive. 


1  These  plants  were  being  grown  by  Dr.  H.  B.  Frost  of  the  Citrus  Experiment 
Station. 


•J!tL'  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION 

TABLE  3 

LARGE  SOUR  ORANGE  NURSERY  SEEDLINGS  GROUPED  IN  CLASSES  ACCORDING  TO 

HEIGHT 


eight  of  classes 

Number  of  plnnts 

in  inches 

of  ouch  size 

3  to     4.5  

0 

5  "      6.5  

5 

7  "      8.5  

5 

9  "    10.5  

9 

11  "    12.5  

11 

13  "    14.5  

30 

15  "    16.5  

37 

17  "    18.5  

<iO 

19  "    20.5  

50 

21  "    22.5  

44 

23  "   24.5  

31 

2o  "    26.5  

15 

27  "    28.5  

3 

29  "    30.5  

1 

31  to  32.5... 

0 

Total  number  of  plants 301 

Average  height,  18.19  inches. 

% 
"What  proportion  of  these  plants  would  be  good  budding  stocks  it 

is  impossible  to  say,  as  they  are  of  unknown  ancestry.  Certainly  it 
seems  to  the  writer  that  all  smaller  than  the  15  to  16.5  inch  class  should 
be  discarded.  This  would  necessitate  the  discarding  of  60  plants  out 
of  the  301  measured. 

At  the  same  time  228  of  the  seedlings  of  the  small  group  were 
measured  and  gave  an  average  height  of  only  9.07  inches,  just  about 
half  the  average  height  of  those  measured  of  the  large  group.  The 
measurements  of  these  228  plants  are  given  below  (Table  4)  grouped 
in  classes  the  same  as  in  the  case  of  the  large  seedlings  as  given  above. 

If  the  same  standard  were  used  in  judging  the  number  of  good 
seedlings  in  this  small  group  that  was  suggested  in  the  group  of  large 
seedlings,  only  24  out  of  the  228  would  remain. 

Another  lot  of  sour  orange  seedlings  separated  in  the  same  way 
into  large  and  small  groups  gave  similar  results.  Similar  segregations 
of  large  and  small  seed-bed  stock  were  also  made  in  Dr.  Frost's  work 
with  seedlings  of  sweet  orange  and  rough  lemon  and  after  they  had 
been  grown  in  the  nursery  a  year  the  rows  planted  with  large  and 
small  seedlings  showed  marked  difference  in  average  size,  nearly  or 
quite  as  marked  as  in  the  case  of  the  sour  orange  seedlings  discussed 
in  detail  above.  It  seems  that  this  inherent  difference  in  the  size 


BULLETIN  317    SELECTION  OF  STOCKS  IN  CITRUS  PROPAGATION 


293 


604 


Fig.  13. — Characteristic  leaves  from  four   different  sweet  orange   seedlings 
representing  very  distinct  types   (natural  size). 


294  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION 

TABLE  4 

SMALL  SOUR  ORANGE  NTRSEKY  SEEDLINGS  GI.OUPED  IN  CLASSES  ACCORDING 

TO  HEIGHT 


Height  o 
in  in 

1  to 
3  " 
5  «' 
7  " 
9  " 
11  " 
13  " 
15  " 
17  " 
19  " 
21  " 

:  elMMI 
chea 

2  5                                    

Number  of  plants 
of  each  size 

5 

4.5                          .     .  .  . 

31 

6.5                

47 

8.5 

27 

105                      

31 

12.5 

33 

14.5 

...:  30 

16.5                         

16 

18.5                       

7 

20.5                 

1 

22.5  ... 

0 

Total  number  of  plants 228 

Average  height,  9.07  inches. 

and  rapidity  of  growth  should  be  given  careful  consideration  in  the 
propagation  of  nursery  stock. 

In  this  nursery  of  only  a  few  thousand  seedlings  each  of  sour, 
sweet,  and  rough  lemons,  many  distinctly  different  types  were  easily 
distinguished  by  marked  taxonomic  characters,  such  as  different  leaf 
shapes  and  different  branching.  While  many  of  the  size  differences 
discussed  above  are  probably  due  to  the  different  genetic  constitutions 
of  the  plants,  part  of  the  difference  in  size  is  doubtless  also  due  to 
variations  in  the  size  of  the  embryos  from  which  different  plants  grew 
and  to  the  local  environments  of  the  various  plants.  There  can  be 
no  doubt,  however,  that  citrus  nursery  stocks  as  ordinarily  grown  are 
made  up  of  a  very  large  number  of  widely  different  types  of  different 
genetic  constitution,  exhibiting  a  wide  range  of  characters. 

The  flowers  of  citrus  fruits  are  showy,  highly  scented,  and  develop 
abundant  nectar,  thus  attracting  bees  and  other  insects  so  that  they 
are  often  cross-pollinated.  It  is  likely  that  almost  all  citrus  plants 
are  of  more  or  less  mixed  heritage  and  would  normally  be  expected  to 
break  up  into  different  types  when  seedlings  are  grown.  The  named 
varieties  are  always  propagated  by  budding  or  grafting  and  do  not 
reproduce  their  characters  in  full  perfection  through  propagation  by 
seeds.  Different  individual  citrus  plants  will  doubtless  be  found  to 
show  different  degrees  of  transmission  of  their  important  characters, 
as  is  the  case  with  practically  all  plants  that  have  been  studied.  Thus 
one  of  the  problems  of  the  future  will  be  to  select  good-  vigorous  stock 


BULLETIN  317    SELECTION  OP  STOCKS  IN  CITRUS  PROPAGATION 


295 


types  of  the  different  species  that  are  found  by  experience  to  transmit 
their  characters  fairly  true  through  the  seed.  When  any  seedling  is 
found  to  be  a  good  stock  type  it  can  be  propagated  by  buds  and  each 
nurseryman  can  grow  enough  trees  to  supply  the  seeds  required  for 
his  nursery  use. 

No  trial  has  been  made  of  these  very  different  types  as  stocks, 
but  it  is  not  reasonable  to  suppose  that  the  dwarfed,  slow-growing 
types  would  make  desirable  stocks.  No  grower  after  seeing  then 
would  think  of  using  them  as  stocks.  Is  it  not  reasonable  to  suppose 
that  their  use  is  in  large  measure  responsible  for  the  different  rates  of 
growth  in  buds  commonly  shown  in  nurseries  ? 


Fig.  14.— Variations  among  sour  orange  seedlings  in  the  same  nursery  row. 
Note  the  difference  in  size,  branching  and  foliage  characters. 


EXAMINATION   OF  EVIDENCE  AND   CONCLUSIONS 

The  writer  concludes  from  the  evidence  at  hand  that  the  differ- 
ences in  size  of  nursery  trees  of  transplanting  age  is  largely  due  to 
the  fact  that  the  seedling  root-stocks  on  which  the  trees  are  budded 
are  of  different  types  possessing  different  inherent  characters  that 
react  differently  on  the  growing  buds.  Vigorous-growing  stocks,  such 
as  the  Florida  rough  lemon,  are  known  to  cause  a  much  more  rapid 
growth  of  buds  of  the  same  variety  than  such  slow-growing  stocks  as 
the  sour  orange  or  trifoliate  orange. 

The  great  influence  that  the  stock  may  cause  on  the  scion  in  citrus 
fruits  is  well  illustrated  by  the  growth  of  Eureka  lemon  on  trifoliate 
orange  stocks  as  shown  by  trees  grown  at  the  Citrus  Experiment 
Station.  At  the  age  of  13  years  the  buds  on  trifoliate  orange  stock,  of 
which  there  are  about  15,  are  not  more  than  one-fifth  the  size  of  those 

DWSION  OF  SUblROPICAL  HORTICULTURE 

COLLEGE  OF  AGRICULTURE 

BERKELEY,  CALIFORNIA 


296  UNIVERSITY   OF   CALIFORNIA  —  EXPERIMENT   STATION 

on  sweet,  sour,  or  grapefruit  stock.  (See  Figs.  7,  8,  9,  and  10,  Bulletin 
267,  pp.  289,  291,  295,  and  297.) 

Without  doubt  some  variation  in  the  size  of  nursery  trees  is  due 
to  the  kinds  of  buds  used,  but  the  buds  in  the  experiments  described 
were  from  selected  trees  known  to  have  produced  uniform  fruit  during 
several  years  and  to  have  shown  no  marked  bud  variations.  Even 
where  buds  are  not  taken  from  specially  selected  trees  they  are  always 
in  practice  taken  from  standard  varieties  which  themselves  originated 
in  each  case  from  a  selected  good  individual.  It  is  not  likely  therefore 
that  more  than  a  minor  part  of  the  variation  in  nursery  trees  is  to 
be  ascribed  to  variations  in  the  buds  used. 

That  variations  in  size  of  different  trees  may  be  caused  by  local 
soil  conditions  or  differences  in  treatment  is  undoubtedly  true,  but 
these  causes,  it  is  believed,  could  not  have  been  responsible  for  all 
the  differences  in  size  of  the  trees  under  experimental  trial.  It  may 
be  that  trees  stunted  or  injured  by  poor  environment  in  the  seed-bed 
or  nursery  would  continue  to  show  this  difference  to  some  extent  after 
being  removed  into  the  permanent  orchard.  The  evidence  available 
is  not  sufficient  to  enable  the  formation  of  a  safe  judgment  as  to  the 
extent  of  such  injury  and  the  length  of  time  it  may  persist  in  perennial 
trees  like  the  various  citrus  species. 

Several  factors  that  have  not  yet  been  discussed  may  also  influence 
the  size  of  the  seedling  and  be  of  considerable  importance  in  this 
connection.  With  many  plants  it  has  been  demonstrated  that  the 
size  of  the  seed  has  a  marked  influence  on  the  growth  of  the  resulting 
seedling.  The  amount  of  reserve  material  in  the  seed  available  to 
start  the  young  plant  in  its  growth  has  a  marked  bearing  in  many 
instances  on  the  total  growth  finally  attained  by  the  plant.  In  citrus 
seeds  more  than  one  embryo  is  developed  commonly  and  frequently 
from  2  to  4  seedlings  are  produced  from  1  seed.  Only  1  of  these 
embryos  develops  from  the  fertilized  egg  cell  in  the  way  normal  with 
most  plants,  the  others  being  developed  as  adventitious  buds  from 
cells  of  the  nucellus  and  are  supposedly  not  effected  by  the  fertiliza- 
tion. Probably  all  of  the  embryos  formed  are  frequently  of  adven- 
titious origin  as  it  has  been  found  that  good  viable  seeds  frequently 
develop  in  fruits  where  pollination  was  prevented.  The  different 
embryos  in  the  same  seed  and  in  different  seeds  always  show  great 
variation  in  size  and  the  seedlings  developing  from  them  starting  with 
such  markedly  different  amounts  of  stored  nourishment  would  be 
expected  to  vary  in  size  for  some  time  if  not  permanently.  The 
writer  has  frequently  observed  that  the  several  seedlings  growing  from 
the'  same  teed,  whenever  this  occurs,  almost  always  differ  markedly 


iO  J23.jv 


BULLETIN  317     SELECTION  OP  STOCKS  IN  CITRUS  PROPAGATION  297 

in  size  in  the  beginning.  Their  comparative  growth  in  later  life, 
however,  has  not  been  observed.  It  seems  probable  that  Blackman's 
"compound  interest  law  of  growth"  would  apply  here  though  the 
investigations  have  all  been  made  with  annual  plants.  Blackman 
states : 

The  dry  weight  attained  by  such  a  plant  (an  annual)  at  the  end  of  any  period 
will  depend  on  (1)  the  weight  of  the  seed  (or  the  seedling  at  its  start),  represent- 
ing the  initial  capital  with  which  the  plant  starts;  (2)  the  average  rate  at  which 
the  plant  makes  use  of  the  material  already  present  to  build  up  new  material, 
this  represents  the  rate  of  interest  on  the  capital  (material)  employed;  (3)  the 
period  of  growth.2 

Doubtless  many  of  the  small  seedlings  in  a  citrus  seed  bed  are  small 
because  they  come  from  small  embryos  and  are  thus  poorly  nourished 
plants  in  the  beginning.  They  start  with  a  small  initial  capital  and 
even  if  their  rate  of  growth  (interest  rate)  was  high  they  could  not 
be  expected  in  a  given  period  to  show  the  same  total  growth  that  a 
good  strong  seedling  would  give. 

Such  small  plants  would  be  at  a  further  disadvantage  in  the  seed 
bed,  fighting  with  their  more  vigorous  neighbors  for  nutrition  and 
light.  If  their  growth  rate  was  only  normal  they  could  not  be  expected 
even  under  good  conditions  to  overtake  the  seedling  that  started  with 
a  good  reserve  capital ;  and  with  the  further  handicap  of  severe  com- 
petition in  the  seed  bed,  they  may  be  permanently  stunted.  It  is 
probable,  furthermore,  that  many  seedlings  that  start  fairly  well  in 
the  beginning  are  injured  and  kept  small  by  overcrowding  in  the 
seed  bed. 

It  may  well  be  questioned  whether  such  dwarfed  seedlings  will  ever 
make  good  stocks,  even  if  they  are  later  given  abundant  room  and 
plenty  of  nourishment.  The  writer  is  not  aware  that  it  has  ever  been 
shown  conclusively  that  dwarfing  from  lack  of  nutrition  and  adverse 
conditions  permanently  affects  the  heritage  of  an  organism,  but  it 
apparently  does  affect  the  individual  in  the  total  growth  that  it  is 
able  to  make  during  its  life.  Even,  therefore,  if  a  part  of  the  small 
seedlings  in  a  nursery  are  due  to  small  embryos  and  poor  environment, 
as  is  undoubtedly  the  case,  this  does  not  change  the  recommendations 
to  be  made  regarding  the  selection  of  nursery  stock,  but  only  further 
emphasizes  its  importance. 

Attention  should  further  be  called  to  the  fact  that  these  small 
seedlings  when  transplanted  to  the  nursery,  are  under  a  further  dis- 


2  J.  H.  Blackman,  The  Compound  Interest  Law  and  Plant  Growths,  Annals  of 
Bot.,  vol.  33,  July,  1919,  pp.  353-360. 

DIVISION  OF  SUBTROPICAL  HORTICULTURE 

COLLEGE  OF  AGRICULTURE 

BERKELEY,  CALIFORNIA 


298  UNIVERSITY   OP   CALIFORNIA — EXPERIMENT   STATION 

advantage  in  that  they  are  usually  much  slower  to  start  growth.  The 
adverse  conditions  in  transplanting  affects  a  small  seedling  more 
severely  than  a  large  one. 

It  must  be  granted  that  if  the  growth  rate  in  the  small  seedling 
was  equal  to  or  greater  than  in  a  large  seedling,  it  might  ultimately 
make  just  as  good  a  stock  when  it  finally  reached  sufficient  size.  It  is 
not  likely,  however,  that  many  of  the  small  seedlings  will  be  found 
to  have  a  specially  rapid  or  large  growth  rate  and  the  difference  in 
size  when  due  to  environment  or  the  size  of  embryo  will  probably  be 
found  to  persist  for  several  years  if  not  during  the  whole  life  cycle 
of  the  plant.  In  view  of  the  doubt  regarding  this  and  the  certainty 
that  many  of  the  small  seedlings  are  small  because  of  their  genetic 
constitution  there  would  seem  to  be  no  question  that  the  wisest  plan 
would  be  to  discard  all  small  seedlings  in  the  seed  bed  and  nursery 
regardless  of  what  has  caused  their  dwarfness. 

The  large  nursery  trees  in  the  experiments  described  continue  to 
show  their  decided  superiority  over  the  intermediate  and  small  trees 
after  a  period  of  2y2  years  in  the  orchard,  when  the  buds  are  41/2 
years  old.  Is  this  condition  of  superiority  likely  to  continue?  So 
far  as  definite  evidence  is  concerned  all  that  can  be  cited  exists  in 
the  trees  themselves  in  that  they  have  continued  superior  during  a  4V&- 
year  period.  It  is  usually  recognized  that  small,  slow-growing  young 
plants  are  likely  to  remain  smaller  than  large,  vigorous  young  plants 
of  the  same  kind.  Dr.  H.  S.  Reed3  in  some  experiments  conducted 
with  sunflowers  at  the  Citrus  Experiment  Station  found  this  relation 
to  exist.  In  this  experiment  a  number  of  young  sunflowers  growing 
under  uniform  conditions  were  numbered  and  measured  in  height 
when  they  were  still  quite  young.  Measurements  were  made  every 
week  thereafter  until  the  plants  reached  maturity.  The  object  of 
the  experiment  as  stated  by  Dr.  Reed  was  "An  attempt  to  discover 
whether  the  large  and  the  small  members  of  the  group  differ  from 
each  other  in  their  growth  rates  as  well  as  in  their  final  size;  to  be 
specific,  whether  the  small  plants  grew  slowly  during  the  entire  season, 
or  whether  they  grew  rapidly  during  their  early  history  and  came 
sooner  to  maturity.  Closely  related  to  this  is  the  question  of  relative 
position  in  the  population  during  the  whole  period  of  growth.  Do 
plants  which  are  undersized  at  the  start  grow  rapidly  enough  to  get 
into  the  higher  groups  as  they  become  older,  or  do  they  remain  under- 
sized to  maturity?"  The  results  obtained  from  the  experiment  showed 


8  Reed,  H.  8.,  Growth   and   variability   in    Helianthus.      American  Journal   of 
Botany,  vol.  6,  June,  1919,  pp.  252-271.  " 


BULLETIN  317     SELECTION  OF  STOCKS  IN  CITRUS  PROPAGATION  299 

that  in  general  plants  that  started  in  a  certain  relative  position  of 
size  showed  a  well  marked  tendency  to  remain  in  the  same  relative 
position  during  the  entire  period  of  growth.  Plants  which  were  small 
at  maturity  were  generally  small  from  the  beginning  and  those  which 
were  large  at  maturity  had  a  well-marked  superiority  from  the  begin- 
ning. Plants  in  general  act  very  much  alike,  and  such  evidence  as 
that  furnished  by  Dr.  Reed's  experiments  with  sunflowers  coupled 
with  the  fact  that  the  groups  of  different-sized  trees  of  the  various 
citrus  varieties  have  retained  their  relative  positions  with  relation  to 
size  during  4  years  is  fairly  strong  evidence  that  the  difference  in 
size  is  likely  to  be  retained  throughout  the  life  of  the  trees. 

Dr.  Reed  concludes  that  the  difference  in  size  of  the  sunflowers 
studied  is  probably  dependent  upon  internal  genetic  factors  rather 
than  upon  external  causal  factors.  That  the  stocks  used  in  citrus 
production  are  or  may  be  of  widely  different  genetic  constitution  is 
clearly  evident  from  the  facts  given  in  this  paper  and  from  evidence 
known  to  every  observant  grower. 

This  indicates  that  to  get  the  best-growing  trees,  only  the  large 
trees  from  a  nursery  should  be  planted  and  under  proper  methods 
this  is  the  policy  that  should  likely  be  pursued.  Some  growers,  how- 
ever, may  think  that  they  have  had  better  success  in  getting  heavy 
yields  with  smaller  trees.  It  is  probably  true  that  with  the  loose 
methods  used  in  the  past  when  neither  buds  nor  stocks  were  selected 
this  might  be  expected.  If  no  selection  of  buds  is  exercised  the  most 
rapidly  growing  nursery  trees  would  likely  be  those  where  the  buds 
were  also  strong  vegetative  growers  at  the  expense  of  fruit  produc- 
tion (Shamel's  shade  types),  but  where  buds  are  taken  from  record 
trees  of  good  fruiting  type,  it  does  not  seem  likely  that  this  will  be 
the  case. 

It  must  be  admitted  that  the  evidence  obtained  is  as  yet  incomplete. 
One  of  the  most  necessary  links  in  the  chain  of  evidence  to  complete 
the  proof  is  to  grow  and  fruit  buds  from  trees,  of  known  record  on 
stocks  of  the  various  types  and  sizes  which  make  up  the  composite 
mixture  that  we  grow  as  sweet  and  sour  orange  stocks  and  the  like. 
This  evidence  is  as  yet  lacking.  We  may  draw  some  evidence  from 
the  reactions  on  scions  caused  by  different  stocks  of  the  same  species, 
as,  for  instance,  the  difference  between  the  Chinese  lemon  and  the 
Florida  rough  lemon.  These  two  lemons  differ  from  each  other  in 
the  same  general  way  as  do  the  different  types  of  the  sour  orange 
described,  and  the  former  has  proven  a  poor  stock  while  the  latter 
has  given  excellent  results. 


300  UNIVERSITY   OP    CALIFORNIA — EXPERIMENT   STATION 

RECOMMENDATIONS 

In  general,  the  evidence  presented  strongly  indicates  that  more 
attention  must  be  given  to  using  stocks  known  to  be  good  vigorous 
growers  and  of  good  type.  If  the  results  of  these  experiments  are 
correctly  interpreted  by  the  writer  it  means  that  our  nursery  methods 
in  citrus  propagation  must  be  materially  changed.  The  following  are 
the  important  suggestions  that  follow  from  the  studies  reported  in 
this  bulletin: 

1.  We  must  no  longer  grow  merely  sour  or  sweet  stocks  and  the 
like  for  budding.    The  process  must  be  carried  further  and  good  stock 
varieties  of  the  sweet  and  sour  orange  must  be  discovered,  named  and 
regularly  grown  to  furnish  seeds  for  growing  nursery  trees.     It  will 
take  a  number  of  years  to  get  comparative  evidence  that  will  enable 
us  finally  to  select  a  few  standard  stock  varieties  just  as  it  has  taken 
us  many  years  to  select  the  Washington  navel  and  the  Valencia  as 
our  two  standard  orange  fruit  varieties.    In  the  meantime,  however,  we 
can  doubtless  greatly  improve  the  product  of  our  stocks  by  using 
seeds  from  selected  trees  of  good  vigorous  growth  and  type  such  as 
the  tree  illustrated  in  Fig.  7.    Nurserymen  should  get  buds  from  some 
tree  of  good  type  known  to  produce  good,  vigorous  and  uniform  seed- 
lings and  bud  enough  trees  to  produce  the  seeds  they  require.    These 
if  possible  should  be  grown  in  a  location  isolated  from  other  citrus 
trees,  to  avoid  cross-pollination.    This  policy  coupled  with  the  selection 
of  the  seedlings  and  nursery  trees  will  doubtless  give  good  results. 

2.  When  transplanting  seed-bed  stock  a  policy  should  be  rigorously 
followed  of  discarding  all  small  individuals.     As  yet  the  evidence  as 
to  what  proportion  of  the  seedlings  should  be  discarded  is  imperfect. 
Doubtless  the  number  that  should  be  discarded  will  vary  in  different 
cases  as  the  seedlings  from  certain  trees  will  probably  be  more  uniform 
than  those  from  others.     In  the  lot  of  seed-bed  stock  described  on 
page  290,  the  smallest  seedlings  were  discarded  before  transplanting 
to  the  nursery,  and  yet  judged  by  size  60  plants  out  of  301  from 
the  large  group  should  be  discarded  and  204  out  of  228  from  the 
group  of  small  seedlings.    This  means  that  aside  from  the  very  small 
seedlings  at  first  discarded,  49  per  cent  more,  judging  by  their  rate 
of  growth,  should  probably  have  been  discarded.     It  may  be  safely 
estimated  that  in  ordinary  lots  of  seedlings  50  per  cent  should  be  dis- 
carded immediately  and  not  planted  in  the  nursery.     Seedlings  from 
the  seed  bed  are  worth  but  little  and  have  cost  little  trouble,  hence,  this 
is  the  place  to  do  the  severe  culling.    The  writer  believes  that  a  severe 
culling  of  the  seedlings  at  the  time  of  transplanting  from  the  seed- 
bed may  unhesitatingly  be  recommended  as  good  policy. 


BULLETIN  317      SELECTION  OF  STOCKS  IN   CITRUS  PROPAGATION  301 

3.  When  budding  a  nursery,  buds  should  never  be  inserted  in  an 
inferior  small  stock.     The  nursery  should  be  carefully  inspected  just 
before  the  budding  starts  and  all  inferior  small  stocks  cut  out.    The 
severity  of  the  culling  at  this  time  should  again  depend  upon  the  range 
of  variation  in  size  found  in  the  nursery  after  the  trees  in  general 
have  reached  the  size  to  bud. 

4.  When  the  buddtd  trees  have  reached  the  age  for  transplanting 
into  the  orchard,  the  nursery  should  be  carefully  inspected  again  and 
all  small,  undersized  buds  cut  out.    Here  again  the  number  of  trees 
to  be  discarded  must  depend  on  the  variation  present  in  the  nursery. 
If  the  stocks  before  budding  have  been  carefully  selected  as  indicated, 
it  is  not  likely  that  a  very  large  percentage  of  the  trees  would  need 
to  be  discarded. 

In  the  nursery  from  which  the  large,  small,  and  intermediate-sized 
buds  were  chosen  for  the  experiment  described  in  this  bulletin,  the 
stocks  had  been  selected  with  much  more  care  than  ordinarily  and 
the  buds  taken  from  good  trees  of  known  record,  yet  about  15  per  cent 
of  the  Washington  navel  trees  were  discarded  and  a  somewhat  smaller 
percentage  of  the  Valencias  and  grapefruits.  A  few  trees  were  trans- 
planted to  the  orchard  that  from  their  growth  since  clearly  show  that 
they  should  have  been  discarded. 

To  those  who  have  read  this  bulletin  with  care  it  will  probably  be 
evident  that  certain  of  the  suggestions  made  are  easily  carried  out  and 
entail  but  little  trouble  and  expense.  The  writer  is  so  thorough!}7 
impressed  with  the  importance  of  the  recommendations  made  that 
he  desires  in  closing  to  emphasize  the  desirability  of  introducing  the 
methods  suggested  as  a  necessary  part  of  the  nursery  methods  pursued 
in  the  citrus  industry.  Citrus  groves  should  last  many  years.  It  is 
poor  policy  to  plant  anything  but  the  best  trees.  We  should  use  only 
the  best  buds,  the  best  stocks  and  the  best  trees. 


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